In a normally closed type electromagnetic fuel injection valve, an electromagnetic actuator as a means for driving a valve element is comprised of a magnetic coil, a stationary core (also referred to as a stationary core or simply as a core) and a movable core (also referred to as an anchor or plunger). When the coil is not energized, the valve element is pressed on a valve seat by a return spring and the valve is kept closed. In this valve closed state, the fuel injection valve has a gap between the movable core and the stationary core. When a driving current is passed through the coil, magnetic flux is generated in a magnetic circuit comprised of the stationary core and the movable core, and the magnetic flux also passes through a gap between the movable core and the stationary core. As a result, a magnetic attractive force is exerted on the movable core. When this magnetic attractive force overcomes a force exerted from the return spring, the movable core moves toward the stationary core.
In a conventional fuel injection valve, it is known that the fuel injection valve has a driving coil energized in the early stage of valve opening operation and a hold coil energized when the valve is held in an open state. Furthermore, it is known in a fuel injection valve device that, by lengthening the time period for which the driving coil is energized, a valve closing speed is reduced due to magnetomotive force that occurs just after the energization of the driving coil is terminated. In the fuel injection valve device, a current passed through the driving coil is large and attractive force in the valve opening direction is also large. Consequently, falling of the attractive force just after the termination of the driving coil energization becomes gentle, and it is possible to reduce the valve closing speed and to reduce an impact from the collision of the valve element with the valve seat when the valve is closed (Claims and specification's 31st paragraph of JP-A-2002-115591).
The above-mentioned conventional art discloses a method for reducing the impact by reducing the valve closing speed before the valve element collides with the valve seat. However it does not consider about the behavior of the valve element or the movable core after the valve element is seated on the valve seat. Even after the valve element collides with the valve seat, the valve element or the movable core does not immediately stop its motion and they continue vibratory motion.
Especially, when a fuel injection valve device is so configured that a movable core or a valve element is separated from each other and the movable core can be moved relative to the valve element, the following takes place: even after the valve element comes into contact with the valve seat in a valve closing operation, the movable core continues an inertial motion relative to the valve element and keeps moving toward the valve seat. This lengthens the time for which the motion of the movable core is terminated. For this reason, it may take some time for the relative positional relation between the movable core and the valve element to return to an initial state in which the valve can be opened.
This problem, though its severity is lower, also arises in constructions in which the movable core and the valve element are joined to each other. More specific description will be given. After the valve element collides with the valve seat, there is a spring-mass system in which the valve element is a spring element and the movable core is a mass element. Therefore, the movable core can continue to move toward the valve seat and is ready to continue vibratory motion. For this reason, it may take some time for the movable core to get into a state in which it can stably carry out the next injection.
As mentioned above, for a fuel injection valve to stably carry out the next injection after it completes one time of injection, it used to be required to wait for a certain time.
An object of the invention is to provide an electromagnetic fuel injection valve device wherein the time from the termination of injection to the start of the next injection can be shortened.